Dr. Terry Bates:

Current Research:

Root Management:

soil pH

Abstract

One- and two-year-old Concord grapevines were used to study the effect of soil pH on vegetative growth and nutrition. Ninety-eight Concord nursery grapevines were planted in 25 gallon pots containing vineyard soil adjusted to a soil pH range of 3.5-7.5. After the first growing season, 49 of the vines were destructively harvested and measured for root and shoot growth. The remaining 49 vines over-wintered in the pots, were defruited in year two, and were destructively harvested at the end of the second growing season. Below 4.5 soil pH, there was a reduction in root biomass and a greater reduction in shoot biomass leading to a higher root to shoot ratio. Higher aluminum availability at low soil pH lead to lower total cation and phosphorus uptake. There were no significant differences in vegetative growth of young Concord vines from a soil pH of 5.0-7.5. However, there was a trend toward lower shoot biomass and higher root to shoot ratio at the highest soil pH level. Phylloxera nodosities were present in equal densities on all roots of the soil pH study; however, the negative impact of phylloxera on vine biomass was only significant on vines already under nutrient stress at the highest and lowest pH treatments.

Introduction

Soils of the Lake Erie Regional Grape Belt can vary in texture, organic matter, pH, aeration, and moisture holding capacity (Feuer et al., 1955). Low soil pH (pH 5.0 or lower), which is characteristic of Lake Erie regional soils, affects nutrient availability and root growth (Feuer et al., 1955; Lathwell and Reid, 1984). Although excessive hydrogen ions in the soil solution can have an effect on root cell membrane potential, low pH itself does not inhibit root growth. As the soil pH decreases from 5 to 3.5, aluminum solubility increases and it is the free and exchangeable aluminum ions that affect nutrient availability and root growth. High free aluminum precipitates phosphorus, making it unavailable to the plant, and exchangeable aluminum displaces calcium and magnesium, decreasing their availability (Foy, 1992). In most plant systems, aluminum toxicity has a direct effect on root growth by inhibiting cell division in the root apical meristem (Kochian, 1995). In spite of this, some species have developed strategies to avoid soil chemical stress and increase nutrient acquisition efficiency.

In response to poor nutrient availability, roots generally have been shown to change growth patterns, to stimulate ion uptake and transport, to modify the rhizosphere chemistry, and to form associations with beneficial microorganisms in order to increase nutrient acquisition efficiency (Waisel et al., 1996). The rhizosphere refers to the root-soil interface and it can differ substantially from the bulk soil in ion concentration, pH, redox potential, root exudates, organic carbon, and microbial activity. Nutrient availability in the bulk soil is a function of the soil chemical characteristics, a passive characteristic. Nutrient availability in the rhizosphere is a function of root physiology and biochemistry, an active process. Differential anion-cation uptake, proton pumping, chelating and reducing compound secretion, and beneficial microbial association are all physiological processes roots use to make the rhizosphere a more benign environment for root growth and ion uptake (Marschner, 1986).

Mycorrhizas are the beneficial association between plant roots and mycorrhizal soil fungi (Koide, 1991). Several studies on vinifera roots document the beneficial association of vesicular-arbuscular mycorrhizae (VAM) in acquiring immobile soil nutrients such as phosphorus (Possingham and Obbink, 1971; Menge et al., 1983; Schubert et al., 1988). VAM infection or its benefit to Concord roots has not been documented.

This study investigates the response of Concord grapevines to soil pH and mild nutrient stress. Attention is given to root growth, rhizosphere pH, nutrient absorption, phylloxera nodosities and mycorrhizae.

Methods

Ninety-eight 25 gallon plastic pots were filled with vineyard soil and pH adjusted with dolomitic limestone or ground sulfur. The native vineyard soil pH was measured at 5.2. Ground sulfur was used to create three soil pH treatments more acidic than 5.2 and dolomitic limestone was used to create three soil pH treatments more alkaline than 5.2. The experiment consisted of seven soil pH treatments x seven replicate pots x 2 growing years = 98 pots total.

Soil from a vacant experimental plot at the Cornell Vineyard Laboratory in Fredonia was mixed with individual pot soil amendments (Table 1) in a cement mixer. After incorporation of the sulfur or lime, the amended soil was dumped into a 25 gallon pot. The pot was placed in a two foot deep trench and a Concord nursery vine was planted in the pot. Drip irrigation was installed on the 98 pots and the vines were kept well watered for the life of the experiment.

In year one, all vines were pruned back to two shoots after the last threat of spring frost. Soil pH and leaf area development were monitored during the first growing season. On 10/6/98, 49 of the pots were destructively harvested. Root fresh weight, shoot fresh weight, bulk soil pH, and rhizosphere pH were measured at harvest. Soil pH was measured with a pH meter in a 50/50 mixture of soil and water by volume. Bulk soil pH was determined from soil collected from an area in the pot without grape roots and rhizosphere pH was determined from soil shaken from the grape roots. After harvest, vine tissues were dried and dry weight was measured. Leaf and petiole samples were taken from the dried tissue and sent to the Penn State Nutrient Analysis Laboratory.

In year two, the remaining vines were pruned to four shoots after the last threat of spring frost. At 30-days-after-bloom, the vines were defruited to remove any crop effects on vegetative growth. On 10/13/99, the second year vines were destructively harvested and measured the same as year-one vines. Additional information was collected on phylloxera and mycorrhizal infection in 1999.

Results

Soil pH had an effect on vine biomass in both 1998 and 1999 (Figure 1 A-D). Below a soil pH of 4.5, there was a decline in total vine dry weight because both root and shoot biomass decreased. At this low soil pH, the root to shoot ratio increased because shoot growth was restricted more than root growth.

From a soil pH of 5 to 7.5, there were no significant differences in vine, shoot, or root biomass. However, slightly higher root biomass and slightly lower shoot biomass at the highest soil pH levels translated to a higher root to shoot ratio.

Figure 1 A-D. The effect of soil pH on the vegetative growth of young Concord grapevines. (n = 6, bars = ± standard error)

Tissue nutrient analysis from 1998 shows the effect of soil pH on Concord vine nutrition (Figure 2 A-B). Low soil pH (< 4.5) decreased the concentration of total cations in grapevine tissue. This was primarily a result of lower potassium and calcium concentrations. In addition, there was an increase in tissue aluminum and iron and a decrease in tissue phosphorus. Above 5.0 soil pH, there was not an effect of soil pH on total tissue cations. However, the addition of dolomitic limestone did cause an increase in tissue magnesium and a decrease in tissue potassium. There was also a decrease in tissue aluminum and iron and an increase in tissue phosphorus at the higher soil pH range.

Figure 2 A and B. The effect of soil pH on one-year-old Concord tissue nutrient concentration. (n = 6, bars = ± standard error)

Although there were no differences in vine size or root:shoot ratio from a soil pH of 5 to 7.5 in the pot study, there were some differences in rhizosphere pH (Figure 3). By comparing the bulk soil pH and the rhizosphere soil pH, vines growing in a bulk soil pH of 4.0 raised the rhizosphere pH over 0.5 pH units. Conversely, vines in a bulk soil pH of 7 decreased the rhizosphere pH by 0.5 pH units. There was little difference between bulk and rhizosphere pH in plants growing in pH 5.5. In well aerated soils, modification of rhizosphere pH is most often attributed to the amount of H+ and HCO3- secreted by the roots as a result of differential cation-anion uptake.

Figure 3: The effect of Concord roots on rhizosphere soil pH. Concord roots in acid soil tended to increase the surrounding soil pH and roots in neutral soil tended to acidify the surrounding soil.

Observations of phylloxera infection in 1998 prompted the measurement of phylloxera nodosities on excavated roots in 1999. Phylloxera nodosities were present on all roots of the soil pH study and there was no effect of soil pH on the density of phylloxera nodosities (average of 37 nodosities/g root dry weight). However, nodosity counts were also variable (from 3 to 120 nodosities/g root dry weight). Therefore, vines were sorted according to soil pH and high nodosity density (> 37 nodosities/g DW) or low nodosity density (< 37 nodosities/g DW). There was an interaction of soil pH and phylloxera infection on shoot dry weight at the highest and lowest soil pH treatments (Figure 4).

Figure 4. The interaction of soil pH and relative phylloxera infection on two-year-old Concord shoot biomass. (n = 6, bars = ± standard error)

Discussion

Soil pH < 4.5: When the soil pH drops below 4.5, the solubility of soil aluminum increases. High soil aluminum displaces cations such as potassium, calcium, and magnesium from the soil solution. This relationship can be seen in this study by the elevated tissue aluminum and decreased tissue potassium and calcium below a soil pH of 4.5. Furthermore, high soil aluminum and iron at low soil pH binds soil phosphorus making it unavailable for plant absorption. High tissue aluminum and iron and low tissue phosphorus illustrate this. Aluminum toxicity can also directly inhibit normal root growth in other plant species. Aluminum toxicity, whether a direct effect on root growth or an indirect effect on nutrient availability, decreases vine biomass and tissue nutrient concentration.

There are a few additional observations worth discussing about Concord vines at low soil pH. The vines raise the rhizosphere pH approximately 0.5 pH units which indicates that the roots are trying to overcome the nutrient stress condition. Low soil pH vines had low wood maturity in year one, poor bud cold-heartiness, and little to no potential crop in year two. There was a significant difference between low soil pH vines of relatively high or low phylloxera infection. The combination of aluminum toxicity and phylloxera infection significantly inhibited vine growth.

Soil pH > 7.0: Although there were no significant differences between vines growing in a soil pH of 5.0 to 7.5, there appears to be a trend toward decreased shoot growth above a soil pH of 7.0 in 1999. There are several possible explanations. It is possible that the addition of excessive rates of dolomitic lime induced potassium deficiency in those plants which decreased shoot growth. However, potassium tissue concentrations did not indicate a major deficiency, there were no leaf symptoms of potassium deficiency, and plant potassium demand should have been lowered with the crop removal. A second possibility may be the occurrence of iron, zinc, or manganese deficiency at the high lime treatment.

At higher soil pH, there was an increase in the root to shoot ratio, a decrease in rhizosphere pH, and a significant effect of high phylloxera infection. These indicate that the vines were responding to a below ground stress.

Soil pH Between 4.5 and 7.0: Looking at vine biomass, tissue nutrient concentrations, rhizosphere pH, and root health, the optimum soil pH for young non-bearing Concord vines appears to be between 5.0 and 6.0. In this soil pH range, the roots do not have to work against poor soil chemical conditions such as aluminum toxicity or phosphorus deficiency. This optimum range is further illustrated by the lack of change in the rhizosphere pH. Adequate root growth and activity in this soil pH range can overcome the negative effects of high phylloxera infection on shoot biomass.

Future Experiments: In the spring of 1999, a new experimental vineyard plot was established at the Fredonia vineyard lab to study the effects of soil pH on Concord grapevine growth and nutrition. The goal is to maximize the production of the Concord grapevines relative to vine size in each soil pH treatment. Results from our soil pH experiment with young potted Concord vines show the effect of soil pH on nutrient availability and vegetative grapevine growth. We predict that the combination of mild nutrient stress (through soil pH) and crop stress (crop nutrient demand) will overtax the root system and lead to both decreased vegetative and reproductive vine growth. Conversely, the soil pH amendment and fertilizer practice that stimulates root growth and activity will be able to sustain higher vegetative and reproductive growth. Since we used dolomitic limestone to adjust the soil pH and we intend on using high crop loads, specific attention will be given to the balance and management of cations (K, Ca, Mg, etc.) in the grapevines.

Feuer, R., Garman, W. L. and Cline, M. G. (1955). Chautauqua County soils. New York State College of Agriculture at Cornell University Soil Association leaflet.

Foy, C. D. (1992). Soil chemical factors limiting plant root growth. Advancements in Soil Science 19: 97-149.

Kochian, L. V. (1995). Cellular mechanisms of aluminum toxicity and resistance in plants. Annual Review in Plant Physiology and Plant Molecular Biology 46: 237-260.

Koide, R. T. (1991). Nutrient supply, nutrient demand and plant response to mycorrhizal infection. New Phytologist 117: 365-385.

Lathwell, D. J. and Reid, W. S. (1984). Crop response to lime in the Northeastern United States. in Soil Acidity and Liming. Adams, F., ed. Madison, Wisconsin, ASA, CSSA, SSSA: 380.

Marschner, H. (1986). Mineral Nutrition of Higher Plants. San Diego, Academic Press Limited.

Menge, J. A., Raski, D. J., Lider, L. A., Johnson, E. L. V., Jones, N. O., Kissler, J. J. and Hemstreet, C. L. (1983). Interactions between mycorrhizal fungi, soil fumigation, and growth of grapes in California. American Journal of Enology and Viticulture 34(2): 117-121.

Possingham, J. V. and Groot Obbink, J. (1971). Endotrophic mycorrhiza and the nutrition of grape vines. Vitis 10: 120-130.

Schubert, A., Cammarata, S. and Eynard, I. (1988). Growth and root colonization of grapevines inoculated with different mycorrhizal endophytes. Horticultural Science 23: 302-303.

Waisel, Y., Eshel, A. and Kafkafi, U. (1996). Plant Roots - The Hidden Half. New York, Marcel Dekker, Inc.